This invention relates to a novel process for carbonylation of acrolein to make exclusively linear esters having one additional carbon atom relative to the starting material. More particularly, the present invention is directed to forming alkyl 4-oxobutyrates and acetals thereof from acrolein or its acetals thereof with carbon monoxide and an alcohol under anhydrous conditions in the presence of palladium catalyst promoted with hydrogen halide or from .beta.-halopropionaldehyde or acetals thereof with carbon monoxide and an alcohol under anhydrous conditions in the presence of palladium catalyst. More specifically, the present invention is directed to forming methyl 4-oxobutyrate and its acetals, methyl 4,4-dimethoxybutyrate and gamma-methoxy-gamma-butyrolactone from the catalyzed reaction of acrolein or its methyl acetals thereof, or from .beta.-chloropropionaldehyde or acetals thereof, carbon monoxide and methanol. Methyl 4-oxobutyrate is a useful intermediate in the production of a variety of industrially useful compounds including gamma-butyrolactone, 1,4-butanediol and glutamic acid.
British Patent No. 1,123,367 to von Kutepow, et al., describes a carbonylation reaction in which an olefin is reacted with carbon monoxide and alcohol in the presence of a catalyst such as palladium dichloride bis(triphenylphosphine) to provide a branched carboxylic acid ester. U.S. Pat. No. 4,245,115 to Butter describes a similar carbonylation employing, as a catalyst, a palladium salt complexed with an arsine or stibine ligand, e.g., palladium dichloride bis(tri-phenylarsine) or palladium dichloride bis(tri-p-tolyl arsine).
Craddock, et al. in U.S. Pat. No. 3,816,488 describe a process for the production of isomeric mixtures of linear and branched carboxylic acids through the reaction of ethylenically unsaturated compounds with carbon monoxide and water in the presence of catalyst compositions of rhodium complexes and compounds and an iodide promoter. In U.S. Pat. No. 3,816,489, Craddock, et al. describe a similar process for the production of isomeric mixtures of linear and branched carboxylic acids through the reaction of ethylenically unsaturated compounds with carbon monoxide and water in the presence of catalyst compositions of iridium complexes and compounds and an iodide promoter.
However, the prior art never devised a procedure to convert acrolein or its acetals to exclusively linear products under carbonylation or hydroformylation conditions, although considerable effort and time have been expended. To date, no one has been successful in making the linear products exclusively. Using the prior art methods, acrolein and its acetals produced mixed isomers, i.e., branched and linear isomers, under hydroformylation and carbonylation conditions. For example, as reported by Botteghi, et al. in the Journal of Molecular Catalysis 40, 129-182 (1987), acrolein or its acetals produce both methyl malonaldehyde and succinaldehyde monoacetals under hydroformylation conditions in the presence of carbon monoxide and hydrogen under various catalytic conditions, e.g., cobalt or rhodium catalysts: ##STR1## Other investigative groups have also found that under hydroformylation conditions, acrolein or its acetals produced mixed isomers. See, e.g., U.S. Pat. Nos. 4,017,550 to Kummer, 3,963,754 to Cumbo, et al., 3,963,755 to Cumbo, et al. and 3,929,915 to Cumbo, et al. Therefore, using the methods of the prior art it is necessary to find a purification method in order to separate the branched and the linear products.
The process of the present invention overcomes the deficiencies of the prior art. Unlike the prior art, the process of the present invention produces exclusively the linear product. Therefore, under the carbonylation conditions of the present invention, the step requiring the separation of the branched from the linear isomers is eliminated. Consequently, the process of the present invention is more economical and efficient, especially in view of the fact that it is the linear isomer which is used to produce 1,4-butanediol, which is an important material for numerous organic syntheses.
Finally, the process according to the present invention has the advantages of good yields and simplicity.